As is well known, heavy duty road vehicles, such as trailer tractors, employ compressed air brake systems. Such heavy duty vehicles are commonly equipped with a turbocharged or supercharged internal combustion engine and the pneumatic brake system obtains its supply of air from the air intake manifold of the vehicle engine where the air is already at superatmospheric pressure, say 25 psig, as a result of supercharging. Such pneumatic or air braking systems generally involve an air compressor operable in normal or unloading modes, a governor for controlling the operating cycle of the air compressor, an air dryer and a reservoir for holding pressurized air for delivery to the vehicle brakes.
When the pressure in the air reservoir falls below a predetermined minimum pressure, say about 100 psig, the compressor governor then causes the air compressor to operate in a normal or loading mode to compress air. The compressed air from the air compressor during its normal or compressing cycle is passed through an air dryer to remove moisture and then into the air brake reservoir or reservoirs. When the desired pressure, say about 120 psig, is attained in the pressurized air reservoir, the compressor governor functions to cause the air compressor to unload (unloading mode).
The air compressor utilized in the braking system requires lubrication, particularly when in the compressing mode. Rather than use an independent lubrication system for the ancillary air compressor, the internal combustion engine with its substantial lubrication system has been used not only to drive the compressor but also to provide lubrication therefor. In such systems, the air compressor is typically mounted on the engine and pressurized lubricating oil is pumped to the air compressor for lubrication while it is compressing and then drains by gravity through a suitable conduit back to the engine oil reservoir.
While the lubricant requirements of the air compressor are small relative to the lubricant requirements of the engine, it is important that the compressor receive adequate lubrication without undue increase in oil consumption. A serious problem which workers in the art have encountered is the build-up of the lubricating oil level in the crankcase of the air compressor.
The undesired build-up of the lubricating oil level in the crank case of the compressor is caused in some applications by the fact that the compressor has to operate at angles and orientations which do not allow the oil to drain back to the engine oil reservoir freely. Also, in some applications, back pressure in the engine oil reservoir does not allow the oil to freely drain back from the compressor.
When the level of lubricating oil in the crankcase of the air compressor becomes high by failure to drain back to the engine oil reservoir, the connecting rods of the compressor impact and dip into the crankcase oil. This in turn increases engine power requirements to drive the air compressor, reduces power available for propelling the vehicle, and is commonly referred to as windage loss.
Oil consumption is also increased because the oil is splashed up around the compressor cylinders and moving pistons, increasing the amount of oil bypassing the rings. Excess oil bypass can be particularly deleterious, quite aside from the oil loss. For example, the bypassed oil may enter the air brake system, gumming up the valves, deteriorating the desiccant in the air dryer, etc., as those skilled in the art will recognize.
Applicant herein recognized that these problems are somewhat analogous to problems encountered with systems employing transmission oil to lubricate axles and the potential for oil build-up in the axle spaces. Applicant further recognized that the long-standing problem of oil build-up in compressors could be solved by analogous techniques employed in the transmission-axle environment, as herein set forth.